1. Field of the Invention
The present invention relates to a projection type display apparatus using a plurality of light valves and, more particularly, to a constituent part mainly including a synthesizing optical system for synthesizing beams projected from respective light valves in the projection type display apparatus.
2. Related Background Art
Such projection type display apparatus as a color projector are used as large-screen image display apparatus and the projection type display apparatus of this type are classified under a method called a single plate method for directly magnifying and projecting a color image and a method called a three plate method for synthesizing images of the three primary colors R (red), G (green), B (blue) and projecting the synthesized image. The three plate method requires more complex apparatus structure than the single plate method, but is easier in color adjustment and more advantageous in color reproduction, resolution, and so on than the single plate type. The three plate method is thus popularly employed in imagery equipment or the like.
An example of such three plate method projection type display apparatus is shown in FIG. 18. White source light including the respective colors R, G, B, emitted from a light source not illustrated, is split into two directions of respective polarization components by polarization beam splitter 11'. Only R light in the component reflected by the polarization beam splitter 11' is transmitted by red transmitting dichroic filter 52 to enter light valve 12R for R signal. The R light is modulated to light having an image signal of R signal and this light travels again through the red transmitting dichroic filter 52 to enter the polarization beam splitter 11'. Only the signal component is extracted from the light in the polarization beam splitter 11' to be outputted. On the other hand, the G light component of the polarized light component transmitted by the polarization beam splitter 11' is reflected to branch off by green reflecting dichroic mirror 51 to enter light valve 12G for G signal. The G light is modulated to light having an image signal of G signal to be reflected. Then the light is again reflected by the green reflecting dichroic mirror 51 to enter the polarization beam splitter 11', in which only the signal component is extracted to be outputted. The B light component in the light transmitted by the green reflecting dichroic mirror 51 is extracted by blue transmitting dichroic filter 53 to enter the light valve for B signal. The B light is modulated to light having an image signal of B signal to be reflected. Then the light travels again through the blue transmitting dichroic filter 53 and then through the green reflecting dichroic mirror 51 to enter the polarization beam splitter 11', in which only the signal component is extracted to be outputted. As a result, the signal components R, G, B are synthesized by the polarization beam splitter 11' and the synthetic light is outputted to be enlarged and projected through projection lens 14 onto a screen not illustrated. Unwanted light components are outputted along the direction of the source light, so that they are not mixed in the synthetic light.
The components of the optical system including these reflection type light valves and polarization beam splitter were mounted individually on a mounting base, e.g. on a mounting base forming a floor member of a housing of the apparatus, thereby achieving the desired placement among the components. In other words, this conventional projection type display apparatus had the structure in which the components were fixed to each other through the mounting base and in which the positional relation among the components was determined through the mounting base. Materials for this mounting base were aluminum alloys, fiber reinforced resins, and so on, which were light in weight and had high workability.